Technology to detect minute quantities of nucleic acids has advanced rapidly over the last two decades including the development of highly sophisticated amplification techniques such as polymerase chain reaction (PCR) and ligase chain reaction (LCR). Researchers have readily recognized the value of such technology to detect diseases and genetic features in human or animal test specimens. The use of probes and primers in such technology is based upon the concept of complementarity, that is, the bonding of two strands of a nucleic acid by hydrogen bonds between complementary nucleotides (also known as nucleotide pairs).
PCR is a significant advance in the art to allow detection of very small concentrations of a targeted nucleic acid. The details of PCR are described, for example, in U.S. Pat. No. 4,683,195 (Mullis et al), U.S. Pat. No. 4,683,202 (Mullis) and U.S. Pat. No. 4,965,188 (Mullis et al), although there is a rapidly expanding volume of literature in this field.
In order to effectively amplify and detect a target nucleic acid, it is usually necessary to isolate that nucleic acid from cellular and other specimen debris. Various lysing procedures are known, including freezing, treatment with digesting enzyme such as proteases (for example, Proteinase K), boiling, use of various detergents (see for example U.S. Ser. No. 178,202, filed Apr. 6, 1988 by Higuchi, and EP-A-0 428 197, published May 22, 1991), solvent precipitations and heating protocols.
Once nucleic acids are extracted, however, there sometime remains a need to separate them from other materials in the lysate due to the presence of inhibitors or interferents in the lysate. One material known to complex with nucleic acids is polyethyleneimine. It has been used to precipitate nucleic acids as contaminants in processes for isolating enzymes such as Q Beta replicase (see U.S. Pat. No. 5,141,857 of DiFrancesco). Affinity columns containing derivatives of polyethyleneimine have also been prepared for capturing nucleic acids, as described for example in U.S. Pat. No. 5,092,992 (Crane et al).
The mere use of polyethyleneimine to precipitate nucleic acids is insufficient to provide target analytes useful for further treatment. The precipitate cannot be used in that form, and release of the nucleic acids from the precipitate is difficult to achieve. Moreover, the nucleic acids which are bound to the polyethyleneimine cannot be amplified using conventional amplification techniques. Thus, a series of problems arise in the selective capture and release of target nucleic acids for subsequent treatment, and no ready solution to those problems is suggested by known procedures.
There remains a need, therefore, for an efficient and simple means for preparing nucleic acids in a sample for amplification or other hybridization procedures.